1. Field of the Invention
The invention relates to analog-to-digital converters and more particularly to such converters wherein the sample-hold and integrate functions are performed by a common circuit arrangement. The converter is applicable to bipolar signals. Further, a technique for automatic gain control is effected when the reference voltage is derived from the input signal.
2. Description of the Prior Art
Analog-to-digital converters have been used extensively in pulse code modulation communication systems to convert continuous time-varying information signals such as, for example, speech signals into a series of on/off pulses. One such encoder is that disclosed in U.S. Pat. No. 3,668,691. FIG. 1 of the subject patent is exemplary and shows separate circuit arrangements for the sample-and-hold, ramp generator and comparator circuits.
Reference may be made to the article, "An Electronic Design Practical Guide to A/D Conversion", Part 2, by Hermann Schmid, Electronic Design, vol. 16, no. 26, Dec. 19, 1968, at pp. 57 - 76. In particular, the discussion on single ramp comparison A/D converters beginning at pp. 58 is exemplary of the prior-art techniques. It should be noted that the discussion assumes some form of sample-and-hold circuit to hold the unknown voltage V.sub.x for comparison with the ramp generator output.